The invention relates to a longitudinally pumped solid-state laser of a high output power and, more particularly, to a solid-state laser in which the laser modes are longitudinally pumpable within the laser-active medium at several sites using pumped beams.
When longitudinally pumping solid-state lasers, particularly by means of laser diodes as a pumping source, the output power is limited either because of the limited available output power of a pumping source or because of temperature effects in the active medium.
This limitation can be bypassed by the use of resonators having several reflection sites within the active medium. It is a problem of the known arrangements of this type that the number of components to be adjusted increases in comparison to linear resonators. This makes handling more difficult and increases the preparation costs. The present invention is therefore based on the object of eliminating the disadvantages of the state of the art.
According to the invention, this object is achieved by a solid-state laser in which the laser modes are longitudinally pumpable within the laser-active medium at several sites by means of pumped beams. An OFF-AXIS multiple path mode situated in a plane given by: ##EQU1## can be excited in a targeted manner by the beaming-in of the pumped light distribution at the site of the intensity maxima. By locally structured loss sites, for example, by means of notches or partial metallizations, other modes can be discriminated. By means of a locally structured reflectivity or transmission of the output mirror, a percentage of an intensity lobe can be decoupled with the frequency of the laser transition of the used active material.
It is an advantage of the present invention that the multipath modes are "OFF-AXIS" in that the modes do not travel along the optical axis in the resonator. This contrasts with conventional "ON-AXIS" modes in which the fundamental mode travels along the optical axis defined by two exterior mirrors in the resonator.
In the case of a conventional ON-AXIS system, the path of the light in the resonator is determined only by the geometry of the resonator mirror which determines the optical axis of the system. By pumping the laser on the optical axis, the fundamental mode is excited. If the pumped light arrangement is removed from the optical axis, higher Gau.beta.-Hermite or Gau.beta.-Laguerre modes will lase. In the case of a fundamental-mode laser, the lasing mode element is a one-dimensional function space. It therefore has no degree of freedom as far as the transversal structure is concerned.
It is an advantage of the present invention that an OFF-AXIS multiple path mode system is used, in which the determining factor is the local distribution of the population inversion in the active medium of the laser resonator. OFF-AXIS multiple paths modes are elements of infinitely dimensional function spaces. From these function spaces, which depend on the resonator geometry, the multiple path mode is excited which has the largest overlap with the inversion distribution, and thus the highest intensification.
It is an advantage of the present invention that a decoupling of only a portion of the local intensity distribution occurs. The present invention is based on the interaction between the locally structured intensifier profile and the locally structured loss mechanisms. This interaction achieves the excitation of the OFF-AXIS multiple path modes and the mode selection in comparison to the Gau.beta.-Hermite and Gau.beta.-Laguerre modes which, in a normal case, have a higher intensification and a reduced inversion. It is also an advantage of Applicants' invention to provide local structuring of the output mirror. The present invention provides an output mirror design having different degrees of reflection or transmission at different sites on the mirror.
Details of the invention are found in the description in which, by means of the drawing, the state of the art and several advantageous embodiments according to the invention are explained.